1. Field of the Invention
The present invention relates to an exhaust gas purification device having an exhaust gas after treatment device in an exhaust passage of an internal combustion engine. Specifically, the present invention relates to detection of erroneous mounting of exhaust temperature sensors provided in the exhaust passage upstream and downstream of a particulate filter.
2. Description of Related Art
A diesel particulate filter (DPF) is attracting attention as an exhaust gas after treatment device of a diesel engine. The DPF is formed with multiple flow passages defined by porous ceramic walls inside. The DPF collects particulate matters contained in exhaust gas when the exhaust gas flowing into the flow passages passes through the porous ceramic walls. The particulate matters collected by the DPF are combusted and eliminated through spontaneous ignition in an operation state, in which temperature of the exhaust gas becomes high, or are compulsorily combusted and eliminated when a deposition amount of the particulate matters reaches a predetermined value. Thus, the DPF can be regenerated and used repeatedly by regularly eliminating the particulate matters.
Multiple exhaust temperature sensors are mounted in the exhaust flow passage upstream and downstream of the DPF for sensing inlet temperature and outlet temperature of the DPF. An ECU calculates the particulate matter deposition amount by using sensing results of the exhaust temperature sensors and performs temperature control during the DPF regeneration. For example, the regeneration is performed by increasing exhaust temperature by performing a post-injection or the like and by maintaining the DPF at temperature capable of combusting the particulate matters.
In order to safely perform the DPF regeneration with high controllability, it is prerequisite that the exhaust temperature sensors operate properly. Therefore, if an abnormality is caused in the exhaust temperature sensors, quick notice to a driver is necessary. Accordingly, various devices for detecting the abnormality have been proposed. For example, generation of an abnormality such as a breakage or a short circuit can be detected by comparing the sensing value of the exhaust temperature sensor with a predetermined value.
A system described in JP-A-2003-149054 has an erroneous detection reducing device applied to an exhaust temperature sensor, which outputs the same value at predetermined temperature as a value outputted when an abnormality occurs. The system improves detection accuracy by performing abnormality determination based on the sensing value only when it is estimated that the temperature is surely higher than the predetermined temperature.
The multiple exhaust temperature sensors used for sensing the temperature have the same sensor structure and characteristics including a connector shape. Connector mounting positions for connecting the exhaust temperature sensors with an engine harness are close to each other. Therefore, there is a possibility that the exhaust temperature sensors, which should be attached to an upstream portion and a downstream portion of the DPF respectively, are mounted in reverse to the intended mounting position.
In this case, the DPF inlet temperature and the DPF outlet temperature recognized by the ECU are mistaken for each other, so estimation accuracy of DPF central temperature or particulate matter deposition amount based on the DPF inlet temperature and the DPF outlet temperature is deteriorated. If the estimation accuracy of the particulate matter deposition amount is deteriorated, there is a possibility that the particulate matters are deposited over an allowable limit and high temperature is caused during the regeneration. Moreover, there is a possibility that the temperature is increased excessively due to deterioration of temperature controllability during the DPF regeneration. As a result, durability of a DPF base material or a catalyst can be degraded, and in the worst case, melt damage of the DPF can be caused. There is a possibility that other control using the DPF temperature or the exhaust temperature is also affected.